Various gypsum products including, but not limited to, wall panels, wallboard, partitions, ceiling, flooring, joint compounds, cementitious compositions and fire-resistant coatings, are popular consumer products which are broadly used in building construction and for other applications.
Commonly, raw gypsum, also known as calcium sulfate dihydrate, terra alba or landplaster, is mined from open and underground mines. When gypsum is mined, the natural rock is found in the dihydrate form, having about two water molecules associated with each molecule of calcium sulfate. In addition to the mined gypsum, synthetic gypsum can be obtained from a byproduct of flue gas desulfurization processes at a power plant. Flue gas that includes sulfur dioxide is wet scrubbed with lime or limestone. Calcium from the lime combines with the sulfur dioxide to form calcium sulfite.CaCO3+SO2→CaSO3+CO2 Via forced oxidation, the calcium sulfite is converted to calcium sulfate.CaSO3+2H2O+½O2→CaSO4.2H2O
In manufacturing gypsum products, mined gypsum or synthetic gypsum is calcined in order to remove water and produce calcined gypsum, also known as Plaster of Paris, stucco, calcium sulfate half-hydrate or calcium sulfate hemihydrate. Calcined gypsum, stucco and hemihydrate are the most commonly used terms, and they are used interchangeably in this application. Gypsum products can be obtained by mixing stucco with water and other components of choice to prepare a gypsum slurry which is formed into various products and is allowed to set.
Sulfur may be present in raw or synthetic gypsum as a contaminant. It can be also present in gypsum products such as wallboard. High amounts of sulfur in a gypsum product are implicated in a variety of housing market complaints related to odors, copper pipe and wiring corrosion, and occupant illness. Thus, it is important to test for the amount of sulfur present in gypsum before the gypsum is used for manufacturing of gypsum products.
A standardized ASTM method D-5504 can be used for detecting reduced sulfur in a gypsum product, however this method requires some stationary and elaborate equipment and is mostly suited for detecting reduced sulfur in a gypsum product. Other available test kits include ULS-Diesel Test Kit from Herguth Laboratories. This test is based on a reaction with potassium permanganate. However, a gypsum sample has to be dissolved first in mineral spirits before the gypsum sample can be tested for sulfur with potassium permanganate.
There is a need for a method by which sulfur can be detected in mined or synthetic gypsum right at the mining site or at the recycling plant and prior to using resources and energy for mining, transporting and calcining gypsum.